<!DOCTYPE html>
<html>
  <head>
    <title>hello world</title>
    <!--指定文档的编码格式为utf-8-->
    <meta charset="UTF-8">
    <!-- 为搜索引擎定义关键词: -->
    <meta name="keywords" content="HTML, CSS, XML, XHTML, JavaScript" />
    <!-- 为网页定义描述内容: -->
    <meta name="description" content="NIIT HTML5 教程" />
    <!-- 定义网页作者: -->
    <meta name="author" content="Jeff" />
    <!-- 每3秒钟刷新当前页面 -->
    <meta http-equiv="refresh" content="3" />
  </head>
</html>
